Battery packaging material, production method therefor, battery, and polyester film

ABSTRACT

A battery packaging material including a laminate that is provided with a barrier layer, a heat-fusible resin layer positioned on one surface side of the barrier layer, and a polyester film positioned on other surface side of barrier layer. This battery packaging material is configured from at least a laminate provided with a barrier layer, heat-fusible resin layer positioned on one surface side of barrier layer, and a polyester film positioned on other surface side of barrier layer. When infrared absorption spectrum on the polyester film&#39;s surface in 18 directions at intervals of 10° from 0°-180° is obtained using total reflection method of Fourier transform infrared spectroscopy, the ratio of the maximum value and the minimum value of the ratio (Y 1340 /Y 1410 ) of the absorption peak intensity Y 1340  in 1340 cm −1  and the absorption peak intensity Y 1410  in 1410 cm −1  in the infrared absorption spectrum is in the range of 1.4-2.7.

TECHNICAL FIELD

The present invention relates to a battery packaging material, a methodfor producing the battery packaging material, a battery, and a polyesterfilm.

BACKGROUND ART

Various types of batteries have been developed heretofore, and in everybattery, a packaging material is an essential member for encapsulating abattery element such as an electrode and an electrolyte. Metallicpackaging materials have often been used for battery packagingheretofore.

On the other hand, in recent years, batteries are being required to bediversified in shape and to be reduced in thickness and weight alongwith improvement in performance of, for example, electric cars, hybridelectric cars, personal computers, cameras, and mobile phones. Metallicbattery packaging materials that have often been used heretofore,however, have trouble in keeping up with diversification in shape andalso have a disadvantage of limiting the reduction in weight.

Thus, in recent years, there has been proposed a film-shaped laminateincluding a base material, a barrier layer, and a heat-sealable resinlayer laminated sequentially, as a battery packaging material that iseasily processed into diverse shapes and is capable of achieving thereduction in thickness and weight (see, for example, Patent Document 1).In such a battery packaging material, generally, a concave portion isformed by cold molding, a battery element such as an electrode and anelectrolytic solution is disposed in a space formed by the concaveportion, and portions of the heat-sealable resin layer are heat-sealedto each other to give a battery with the battery element stored in thebattery packaging material.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: Japanese Patent Laid-open Publication No.    2008-287971

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In recent years, a battery packaging material is being required to befurthermore reduced in film thickness, along with a requirement ofreducing the size and the thickness of batteries.

However, when the thickness of each layer in the battery packagingmaterial decreases, a peripheral edge of a concave portion formed on thebattery packaging material is curled (curved), so that storage of abattery element and heat sealing of a heat-sealable resin layer aresometimes hindered, leading to deterioration of production efficiency ofbatteries. Particularly, a battery packaging material to be used in alarge secondary battery such as a secondary battery for use in cars hasa problem that since the battery packaging material has a large size,the impact of curling on productivity of batteries is very large.

Further, as regards a battery having its outer surface (surface of abase material) formed of, for example, a nylon film, attachment of anelectrolytic solution to the surface of the battery in a step ofproducing the battery affects (whitens) the outer surface of the batteryto make the battery a defect. Therefore, in order to improve chemicalresistance and electrolytic solution resistance of the outer surface ofa battery, a stretched polyester film is sometimes used as a basematerial. The present inventors, however, have found that a batterypackaging material including a laminated stretched polyester filmparticularly easily generates the curling. Further, the batterypackaging material with a small thickness has a problem of easilydecreasing its moldability. In particular, the stretched polyester filmhas a problem of being harder than a polyamide film and thus beinginferior in moldability.

Under such circumstances, a main object of the present invention is toprovide a technique of improving the moldability and minimizing curlingafter molding of a battery packaging material that includes a laminatehaving a barrier layer, a heat-sealable resin layer situated on onesurface side of the barrier layer, and a polyester film situated on theother surface side of the barrier layer.

Means for Solving the Problems

The present inventors have extensively conducted studies to solve theabove-mentioned problems. As a result, the present inventors have foundthat as regards a battery packaging material that includes a laminatehaving at least a barrier layer, a heat-sealable resin layer situated onone surface side of the barrier layer, and a polyester film situated onthe other surface side of the barrier layer, the battery packagingmaterial is excellent in moldability and effectively minimizes curlingafter molding when the polyester film has a ratio in a range of 1.4 ormore and 2.7 or less between a maximum value Y_(max) and a minimum valueY_(min) (degree of surface orientation: Y_(max)/Y_(min)), with themaximum value Y_(max) and the minimum value Y_(min) respectivelyrepresenting a maximum value and a minimum value of a ratio between anabsorption peak intensity Y₁₃₄₀ at 1340 cm⁻¹ and an absorption peakintensity Y₁₄₁₀ at 1410 cm¹ (Y₁₃₄₀/Y₁₄₁₀) in infrared absorption spectraacquired for 18 directions at intervals of 10° from 00 to 1800 on asurface of the polyester film according to attenuated total reflectionof Fourier transform infrared spectroscopy. The present invention hasbeen completed by further conducting repetitive studies based on thesefindings.

That is, the present invention provides an invention with the aspectsdescribed below.

Item 1. A battery packaging material including a laminate that has atleast a barrier layer, a heat-sealable resin layer situated on onesurface side of the barrier layer, and a polyester film situated on theother surface side of the barrier layer, the polyester film having aratio in a range of 1.4 or more and 2.7 or less between a maximum valueY_(max) and a minimum value Y_(min) (degree of surface orientation:Y_(max)/Y_(min)), with the maximum value Y_(max) and the minimum valueY_(min) respectively representing a maximum value and a minimum value ofa ratio between an absorption peak intensity Y₁₃₄₀ at 1340 cm⁻¹ and anabsorption peak intensity Y₁₄₁₀ at 1410 cm⁻¹ (Y₁₃₄₀/Y₁₄₁₀) in infraredabsorption spectra acquired for 18 directions at intervals of 10° from0° to 180° on a surface of the polyester film according to attenuatedtotal reflection of Fourier transform infrared spectroscopy.

Item 2. The battery packaging material according to item 1, wherein aratio of thickness of the heat-sealable resin layer to thickness of thepolyester film is less than 3.

Item 3. The battery packaging material according to item 1 or 2, whereinthe heat-sealable resin layer has a thickness of 100 μm or less.

Item 4. The battery packaging material according to any one of items 1to 3, wherein the polyester film has a birefringence index of 0.016 ormore.

Item 5. A battery including: a battery element that has at least apositive electrode, a negative electrode, and an electrolyte; andpackaging that is formed of the battery packaging material according toany one of items 1 to 4 and stores the battery element therein.

Item 6. A method for producing a battery packaging material, the methodincluding:

a step of obtaining a laminate by laminating at least a polyester film,a barrier layer, and a heat-sealable resin layer in this order, and

using, as the polyester film, a polyester film having a ratio in a rangeof 1.4 or more and 2.7 or less between a maximum value Y_(max) and aminimum value Y_(min) (degree of surface orientation: Y_(max)/Y_(min)),with the maximum value Y_(max) and the minimum value Y_(min)respectively representing a maximum value and a minimum value of a ratiobetween an absorption peak intensity Y₁₃₄₀ at 1340 cm⁻¹ and anabsorption peak intensity Y₁₄₁₀ at 1410 cm⁻¹ (Y₁₃₄₀/Y₁₄₁₀) in infraredabsorption spectra acquired for 18 directions at intervals of 10° from0° to 180° on a surface of the polyester film according to attenuatedtotal reflection of Fourier transform infrared spectroscopy.

Item 7. A polyester film used in a battery packaging material, thepolyester film having a ratio in a range of 1.4 or more and 2.7 or lessbetween a maximum value Y_(max) and a minimum value Y_(min) (degree ofsurface orientation: Y_(max)/Y_(min)), with the maximum value Y_(max),and the minimum value Y_(min) respectively representing a maximum valueand a minimum value of a ratio between an absorption peak intensityY₁₃₄₀ at 1340 cm⁻¹ and an absorption peak intensity Y₁₄₁₀ at 1410 cm⁻¹(Y₁₃₄₀/Y₁₄₁₀) in infrared absorption spectra acquired for 18 directionsat intervals of 10° from 00 to 1800 on a surface of the polyester filmaccording to attenuated total reflection of Fourier transform infraredspectroscopy.

Item 8. Use of a polyester film in a battery packaging material, thepolyester film having a ratio in a range of 1.4 or more and 2.7 or lessbetween a maximum value Y_(max) and a minimum value Y_(min) (degree ofsurface orientation: Y_(max)/Y_(min)), with the maximum value Y_(max)and the minimum value Y_(min) respectively representing a maximum valueand a minimum value of a ratio between an absorption peak intensityY₁₃₄₀ at 1340 cm⁻¹ and an absorption peak intensity Y₁₄₁₀ at 1410 cm⁻¹(Y₁₃₄₀/Y₁₄₁₀) in infrared absorption spectra acquired for 18 directionsat intervals of 10° from 00 to 1800 on a surface of the polyester filmaccording to attenuated total reflection of Fourier transform infraredspectroscopy.

Advantages of the Invention

According to the present invention, it is possible to provide a batterypackaging material that includes a laminate having a barrier layer, aheat-sealable resin layer situated on one surface side of the barrierlayer, and a polyester film situated on the other surface side of thebarrier layer and that is excellent in moldability and effectivelyminimizes curling after molding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing one exemplified cross-sectional structure of abattery packaging material according to the present invention.

FIG. 2 is a view showing one exemplified cross-sectional structure ofthe battery packaging material according to the present invention.

FIG. 3 is a view showing one exemplified cross-sectional structure ofthe battery packaging material according to the present invention.

FIG. 4 is a view showing one exemplified cross-sectional structure ofthe battery packaging material according to the present invention.

FIG. 5 is a schematic view for illustrating a method for evaluatingcurling.

FIG. 6 is a schematic view for illustrating the method for evaluatingcurling.

EMBODIMENTS OF THE INVENTION

A battery packaging material according to the present invention ischaracterized by including a laminate that has at least a barrier layer,a heat-sealable resin layer situated on one surface side of the barrierlayer, and a polyester film situated on the other surface side of thebarrier layer, the polyester film having a ratio in a range of 1.4 ormore and 2.7 or less between a maximum value Y_(max) and a minimum valueY_(min) (degree of surface orientation: Y_(max)/Y_(min)), with themaximum value Y_(max) and the minimum value Y_(min) respectivelyrepresenting a maximum value and a minimum value of a ratio between anabsorption peak intensity Y₁₃₄₀ at 1340 cm⁻¹ (CH₂ wagging vibration) andan absorption peak intensity Y₁₄₁₀ at 1410 cm⁻¹ (C═C stretchingvibration) (Y₁₃₄₀/Y₁₄₁₀) in infrared absorption spectra acquired for 18directions at intervals of 10° from 0° to 180° on a surface of thepolyester film according to attenuated total reflection of Fouriertransform infrared spectroscopy. Hereinafter, the battery packagingmaterial according to the present invention is described in detail.

In the present specification, the expression of a numerical range“(from) a value to a value” represents the value on the left side ormore and the value on the right side or less. For example, theexpression of a numerical range “(from) X to Y” means X or more and Y orless.

1. Laminated Structure of Battery Packaging Material

A battery packaging material 10 according to the present inventionincludes, as shown in FIG. 1, a laminate having, for example, apolyester film 1, a barrier layer 3, and a heat-sealable resin layer 4in this order. In the battery packaging material according to thepresent invention, the polyester film 1 is disposed on a batterypackaging material's outermost-layer side and the heat-sealable resinlayer 4 is an innermost layer. That is, portions of the heat-sealableresin layer 4 that are situated on a periphery of a battery element areheat-sealed to each other to hermetically seal the battery element inthe heat-sealable resin layer during assembly of a battery, so that thebattery element is encapsulated.

As shown in FIG. 2, the battery packaging material according to thepresent invention may include, for example, an adhesive agent layer 2between the polyester film 1 and the barrier layer 3 as necessary forthe purpose of increasing the adhesiveness between these layers. Anadhesive layer 5 may be provided between the barrier layer 3 and theheat-sealable resin layer 4 as necessary for the purpose of increasingthe adhesiveness between these layers. Further, as shown in FIG. 4, forexample, a surface coating layer 6 may be provided on an exterior of thepolyester film 1 (opposite to the heat-sealable resin layer 4) asnecessary.

The total thickness of the laminate that forms the battery packagingmaterial according to the present invention is not particularly limitedbut is, for example, preferably about 160 μm or less, more preferablyabout 35 to 155 μm, further preferably about 45 to 120 μm, from aviewpoint of reducing the total thickness of the laminate to the minimumpossible, allowing the battery packaging material to exhibit highmoldability, and further effectively minimizing curling after molding.Even when the laminate that forms the battery packaging materialaccording to the present invention has a thickness of as small as, forexample, 160 μm or less, the present invention allows the batterypackaging material to have excellent moldability and is capable ofeffectively minimizing curling after molding.

2. Layers Forming Battery Packaging Material [Polyester Film 1]

In the battery packaging material according to the present invention,the polyester film 1 is a layer that is situated on a battery packagingmaterial's outermost-layer side and functions as a base material.

In the battery packaging material according to the present invention,the polyester film has a ratio in a range of 1.4 to 2.7 between amaximum value Y_(max) and a minimum value Y_(min) (degree of surfaceorientation: Y_(max)/Y_(min)), with the maximum value Y_(max) and theminimum value Y_(min) respectively representing a maximum value and aminimum value of a ratio between an absorption peak intensity Y₁₃₄₀ at1340 cm⁻¹ (CH₂ wagging vibration) and an absorption peak intensity Y₁₄₁₀at 1410 cm⁻¹ (C═C stretching vibration) (Y₁₃₄₀/Y₁₄₁₀) in infraredabsorption spectra acquired for 18 directions at intervals of 10° from0° to 180° on a surface of the polyester film according to attenuatedtotal reflection of Fourier transform infrared spectroscopy. With thepolyester film having a degree of surface orientation (Y_(max)/Y_(min))in the range of 1.4 to 2.7, the battery packaging material according tothe present invention is excellent in moldability and furthereffectively minimizes curling after molding. This mechanism isconsidered to be as follows. That is, since the polyester film has adegree of surface orientation (Y_(max)/Y_(min)) in the range of 1.4 to2.7, polyester molecules that form the polyester film are considered tohave high crystal orientation to suppress contraction of the polyesterfilm during molding, resulting in allowing the battery packagingmaterial to exhibit excellent moldability and effectively minimizecurling after molding.

Specific conditions for measuring the infrared absorption spectra are asfollows. The measurement of the infrared absorption spectra on thesurface of the polyester film can be performed for a polyester filmlaminated in the battery packaging material as long as the surface ofthe polyester film is exposed. When, for example, the surface coatinglayer 6 described later is laminated on the surface of the polyesterfilm 1, the surface coating layer 6 is removed to expose the surface ofthe polyester film and then the measurement can be performed. Thefollowing measurement of the infrared absorption spectra for thepolyester film of the present invention is performed for a polyesterfilm as a single layer under the measurement conditions described below.

(Conditions for Measuring Infrared Absorption Spectra)

The measurement is performed with a Fourier transform infraredspectrophotometer under the following conditions according to singlereflection ATR.

Wavenumber resolution: 8 cm-1

IRE: Ge

Angle of incidence: 30°Polarizer: wire grid, S polarizationBaseline: average value of intensity in a wavenumber range of 1800 cm-1to 2000 cm-1Absorption peak intensity Y₁₃₄₀: value obtained by deducting value ofbaseline from maximum value of peak intensity in wavenumber range of1335 cm-1 to 1342 cm-1Absorption peak intensity Y₁₄₁₀: value obtained by deducting value ofbaseline from maximum value of peak intensity in wavenumber range of1400 cm-1 to 1410 cm-1

Acquisition of the infrared absorption spectra for 18 directions wasperformed by horizontally placing a polyester film as a sample on asample holder and rotating the sample together with a Ge crystal placedon the sample by 10°. The angel of incidence is an angle between avertical line (normal) and incident light.

The degree of surface orientation (Y_(max)/Y_(min)) is not particularlylimited as long as it is in the range of 1.4 to 2.7. The degree ofsurface orientation, however, is, for example, preferably about 1.6 ormore as a lower limit and is, for example, preferably about 2.4 or lessas an upper limit, from a viewpoint of improving the moldability as wellas allowing the battery packaging material to have excellent moldabilityand minimizing curling after molding. The degree of surface orientation(Y_(max)/Y_(min)) preferably ranges from about 1.4 to about 2.4, fromabout 1.6 to about 2.7, from about 1.6 to about 2.4, for example.

The polyester film having such a degree of surface orientation:Y_(max)/Y_(min) can be produced by appropriately adjusting, for example,a stretching method, a stretching ratio, stretching speed, coolingtemperature, and heat setting temperature during production of thepolyester film.

In the battery packaging material according to the present invention,the polyester film preferably has a birefringence index of 0.016 ormore. That is, the birefringence index (nx-ny) is preferably 0.016 ormore that is calculated from measured refractive indexes, one of whichis a refractive index (nx) along a slow axis having a large refractiveindex and the other of which is a refractive index (ny) along a fastaxis orthogonal to the slow axis in measurement of the refractiveindexes for the polyester film. The polyester film having abirefringence index of 0.016 or more allows the battery packagingmaterial to exhibit more excellent moldability and furthermoreeffectively minimize curling after molding. This mechanism is consideredto be as follows. That is, since the polyester film has a birefringenceindex of 0.016 or more, polyester molecules that form the polyester filmare considered to have high crystal orientation to suppress contractionof the polyester film during molding, resulting in allowing the batterypackaging material to exhibit more excellent moldability and furthermoreeffectively minimize curling after molding.

Specific conditions for measuring the birefringence index are asfollows. The measurement of the birefringence index for the polyesterfilm is performed for a polyester film used in the battery packagingmaterial.

(Conditions for Measuring Birefringence Index)

The birefringence index of the polyester film can be measured using aphase difference measuring apparatus. The measurement wavelength is setto 550 nm and the angle of incidence is set to 10 degrees. The thicknessof the polyester film used for calculation of the birefringence index ismeasured using a micrometer. An average refractive index of thepolyester film used for calculation of the birefringence index is set toan assumed value of 1.6200.

The birefringence index is, for example, preferably about 0.019 or moreas a lower limit and is, for example, preferably about 0.056 or less,more preferably about 0.050 or less, further preferably about 0.042 orless, further preferably about 0.026 or less, particularly preferablyabout 0.022 or less as an upper limit, from a viewpoint of furthermoreimproving the moldability as well as minimizing curling after molding.The birefringence index preferably ranges from about 0.016 to about0.056, from about 0.016 to about 0.050, from about 0.016 to about 0.042,from about 0.016 to about 0.026, from about 0.016 to about 0.022, fromabout 0.019 to about 0.056, from about 0.019 to about 0.050, from about0.019 to about 0.042, from about 0.019 to about 0.026, from about 0.019to about 0.022, for example.

The refractive index (nx) along the slow axis of the polyester film ispreferably about 1.68 to about 1.70. The refractive index (ny) along thefast axis of the polyester film is preferably about 1.64 to about 1.68.

The polyester film having such a birefringence index can be produced, asin the case of the polyester film having the degree of surfaceorientation: Y_(max)/Y_(min) described above, by appropriatelyadjusting, for example, the stretching method, the stretching ratio, thestretching speed, the cooling temperature, and the heat settingtemperature during production of the polyester film.

The polyester film is preferably a stretched polyester film, morepreferably a biaxially stretched polyester film. The stretched polyesterfilm is a polyester film stretched in a process of producing thepolyester film.

Specific examples of polyester that forms the polyester film includepolyethylene terephthalate, polybutylene terephthalate, polyethylenenaphthalate, polybutylene naphthalate, polyethylene isophthalate,copolyester with ethylene terephthalate as a main repeating unit, andcopolyester with butylene terephthalate as a main repeating unit.Specific examples of the copolyester with ethylene terephthalate as amain repeating unit include copolymer polyester obtained by polymerizingethylene terephthalate as a main repeating unit with ethyleneisophthalate (abbreviated as polyethylene (terephthalate/isophthalate)and the same applies hereinafter), polyethylene(terephthalate/isophthalate), polyethylene (terephthalate/adipate),polyethylene (terephthalate/sodium sulfoisophthalate), polyethylene(terephthalate/sodium isophthalate), polyethylene(terephthalate/phenyl-dicarboxylate), and polyethylene(terephthalate/decane dicarboxylate). Specific examples of thecopolyester with butylene terephthalate as a main repeating unit includecopolymer polyester obtained by polymerizing butylene terephthalate as amain repeating unit with butylene isophthalate (abbreviated aspolybutylene(terephthalate/isophthalate) and the same applieshereinafter), polybutylene (terephthalate/adipate), polybutylene(terephthalate/sebacate), polybutylene (terephthalate/decanedicarboxylate), and polybutylene naphthalate. These types of polyestermay be used alone or in combination of two or more thereof.

The thickness of the polyester film 1 is not particularly limited butis, for example, preferably 50 μm or less from a viewpoint of improvingthe moldability and effectively minimizing curling after molding. Thethickness of the polyester film 1 is, for example, preferably about 4 to30 μm, more preferably about 16 to 25 μm, from a viewpoint offurthermore increasing the moldability as well as minimizing curling.When the polyester film 1 has a multilayer structure as described later,the thickness of one polyester film layer situated on the batterypackaging material's outermost-layer side is, for example, preferablyabout 4 to 16 μm, more preferably about 9 to 12 μm.

The polyester film 1 may have a single layer or multiple layers(multilayer structure). When the polyester film 1 has multiple layers,at least one polyester film layer situated on the battery packagingmaterial's outermost-layer side (opposite to the barrier layer 3) maysatisfy the range of the degree of surface orientation: Y_(max)/Y_(min)described above.

In order to improve pinhole resistance and insulation quality when thebattery packaging material is formed into packaging of a battery, it isalso possible to form the base material by laminating, in addition tothe polyester film, at least one of a different material resin film orcoating (formation of a multilayer structure) on the one surface side ofthe barrier layer 3. Examples of another resin film used for the basematerial include a resin film formed of, for example, a polyamide, anepoxy resin, an acrylic resin, fluororesin, polyurethane, a siliconeresin, a phenolic resin, a polyether imide, a polyimide, or mixtures orcopolymerized products thereof. Specific examples of the structureincluding the polyester film 1 and the different material resin filmformed into lamination include a multilayer structure including thepolyester film and a polyamide film laminated on top of another.

Specific examples of a polyamide that forms the polyamide film includealiphatic polyamides such as nylon 6, nylon 66, nylon 610, nylon 12,nylon 46, and a copolymer of nylon 6 with nylon 6,6; aromatic-containingpolyamides such as a hexamethylenediamine-isophthalic acid-terephthalicacid copolymerized polyamide (e.g., nylon 6I, nylon 6T, nylon 6IT, andnylon 6I6T (I represents isophthalic acid and T represents terephthalicacid) having a structural unit derived from terephthalic acid and/orisophthalic acid) and polymethaxylylene adipamide (MXD6); alicyclicpolyamides such as polyaminomethyl cyclohexyl adipamide (PACM 6); apolyamide obtained by copolymerizing a lactam component with anisocyanate component such as 4,4′-diphenylmethane-diisocyanate, and apolyester amide copolymer and a polyether ester amide copolymer as acopolymer of a copolymerized polyamide with polyester or polyalkyleneether glycol; and copolymers thereof. These polyamides may be used aloneor in combination of two or more thereof. The polyamide film isexcellent in stretchability and capable of preventing generation ofwhitening caused by resin breakage during molding and is thus suitablyused as the resin film used together with the polyester film 1 for thebase material.

As specific examples of the cases in which the base material is thepolyester film 1 having a multilayer structure and in which the basematerial includes the resin film, preferred are a laminate including apolyester film and a nylon film, and a laminate including a plurality ofpolyester films laminated on top of another, more preferred are alaminate including a stretched polyester film and a stretched nylonfilm, and a laminate including a plurality of stretched polyester filmslaminated on top of another. For example, when having a two-layerstructure, the base material is preferably configured to include thepolyester film and a polyamide film laminated on top of another orconfigured to include the polyester film and the polyester filmlaminated on top of another, and the base material is more preferablyconfigured to include polyethylene terephthalate and nylon laminated ontop of another or configured to include polyethylene terephthalate andpolyethylene terephthalate laminated on top of another. The polyesterfilm is less likely to be discolored even when, for example, anelectrolytic solution is attached to a surface thereof, so that the basematerial can be formed into a laminate including a nylon film and thepolyester film in this order from a base material's barrier-layer 3 sideto be configured to have excellent electrolytic solution resistance. Forexample, 3 to 25 μm is preferable thickness of the polyester film notsituated as the outermost layer or the resin film other than thepolyester film.

When the base material is formed as the polyester film 1 having amultilayer structure or when the base material is configured to includethe resin film, the polyester film 1 or the resin film may be bonded toanother film with an adhesive agent interposed therebetween, or thepolyester film 1 or the resin film may be directly laminated on anotherfilm without an adhesive agent interposed therebetween. Examples of amethod for bonding the films without an adhesive agent interposedtherebetween include methods of bonding the films in a heat-meltedstate, such as a coextrusion method, a sandwich lamination method, and athermal lamination method. When the films are bonded with an adhesiveagent interposed therebetween, the adhesive agent to be used may be atwo-liquid curable adhesive agent or a one-liquid curable adhesiveagent. An adhesive mechanism of the adhesive agent is not particularlylimited and may be any one of a chemical reaction type, a solventvolatilization type, a heat melting type, a heat pressing type, anelectron beam curing type, an ultraviolet curing type, and the like.Specific examples of the adhesive agent include the same adhesive agentsas exemplified for the adhesive agent layer 2. The thickness of theadhesive agent can also be set as in the adhesive agent layer 2.

In the present invention, a lubricant is preferably attached to asurface of the battery packaging material from a viewpoint of increasingthe moldability of the battery packaging material. The lubricant may becontained in the polyester film 1 or the surface coating layer 6 or mayexist on a surface of the battery packaging material. The lubricantexisting on a front surface of the battery packaging material may be oneoozed out from a lubricant contained in a resin that forms the polyesterfilm 1 or the surface coating layer 6, or one applied to a surface ofthe battery packaging material. The lubricant is not particularlylimited but is preferably an amide-based lubricant. Specific examples ofthe lubricant include a saturated fatty acid amide, an unsaturated fattyacid amide, a substituted amide, a methylol amide, a saturated fattyacid bis-amide, and an unsaturated fatty acid bis-amide. Specificexamples of the saturated fatty acid amide include lauric acid amide,palmitic acid amide, stearic acid amide, behenic acid amide, andhydroxystearic acid amide. Specific examples of the unsaturated fattyacid amide include oleic acid amide and erucic acid amide. Specificexamples of the substituted amide include N-oleylpalmitic acid amide,N-stearylstearic acid amide, N-stearyloleic acid amide, N-oleylstearicacid amide, and N-stearylerucic acid amide. Specific examples of themethylol amide include methylolstearic acid amide. Specific examples ofthe saturated fatty acid bis-amide include methylene-bis-stearic acidamide, ethylene-bis-capric acid amide, ethylene-bis-lauric acid amide,ethylene-bis-stearic acid amide, ethylene-bis-hydroxystearic acid amide,ethylene-bis-behenic acid amide, hexamethylene-bis-stearic acid amide,hexamethylene-bis-behenic acid amide, hexamethylene-hydroxystearic acidamide, N,N′-distearyladipic acid amide, and N,N′-distearylsebacic acidamide. Specific examples of the unsaturated fatty acid bis-amide includeethylene-bis-oleic acid amide, ethylene-bis-erucic acid amide,hexamethylene-bis-oleic acid amide, N,N′-dioleyladipic acid amide, andN,N′-dioleylsebacic acid amide. Specific examples of the fatty acidester amide include stearamide ethyl stearate. Specific examples of thearomatic bis-amide include m-xylylene-bis-stearic acid amide,m-xylylene-bis-hydroxystearic acid amide, and N,N′-distearylisophthalicacid amide. The lubricant may be used alone or in combination of two ormore thereof.

When the lubricant exists on a surface of the polyester film 1, theabundance of the lubricant is not particularly limited but is, forexample, preferably about 3 mg/m² or more, more preferably about 4 to 15mg/m², further preferably about 5 to 14 mg/m² in an environment at atemperature of 24° C. and a relative humidity of 60%.

The total thickness of the polyester film 1 and the other resin film(total thickness of the base material) is not particularly limited butis, for example, preferably about 50 μm or less from a viewpoint ofincreasing the moldability and effectively minimizing curling aftermolding. The thickness of the polyester film 1 is, for example,preferably about 4 to 30 μm, more preferably about 16 to 25 μm, from aviewpoint of furthermore increasing the moldability as well asminimizing curling.

[Adhesive Agent Layer 2]

In the battery packaging material according to the present invention,the adhesive agent layer 2 is a layer provided between the polyesterfilm 1 or the resin film and the barrier layer 3 as necessary, forstrongly bonding these layers to each other.

The adhesive agent layer 2 is formed of an adhesive agent capable ofbonding the polyester film 1 or the resin film to the barrier layer 3.The adhesive agent used for forming the adhesive agent layer 2 may be atwo-liquid curable adhesive agent or a one-liquid curable adhesiveagent. Further, the adhesive agent used for forming the adhesive agentlayer 2 is not particularly limited and may be any one of a chemicalreaction type, a solvent volatilization type, a heat melting type, aheat pressing type, and the like.

Specific examples of the adhesive component that can be used for formingthe adhesive agent layer 2 include polyester-based resins such aspolyethylene terephthalate, polybutylene terephthalate, polyethylenenaphthalate, polybutylene naphthalate, polyethylene isophthalate, andcopolyester; a polyether-based adhesive agent; a polyurethane-basedadhesive agent; an epoxy-based resin; a phenol-based resin;polyamide-based resins such as nylon 6, nylon 66, nylon 12, and acopolyamide; polyolefin-based resins such as a polyolefin, a carboxylicacid-modified polyolefin, and a metal-modified polyolefin, and apolyvinyl acetate-based resin; a cellulose-based adhesive agent; a(meth)acrylic-based resin; a polyimide-based resin; polycarbonate; aminoresins such as a urea resin and a melamine resin; rubber such aschloroprene rubber, nitrile rubber, and styrene-butadiene rubber; and asilicone-based resin. These adhesive components may be used alone or incombination of two or more thereof. Among these adhesive components, apolyurethane-based adhesive agent is preferred, for example. Theseresins to be an adhesive component can be used in combination with anappropriate curing agent to increase the adhesive strength. The curingagent is appropriately selected from, for example, a polyisocyanate, apolyfunctional epoxy resin, an oxazoline group-containing polymer, apolyamine resin, and an acid anhydride according to a functional groupof the adhesive component. Preferable examples of these adhesivecomponent and curing agent include a polyurethane-based adhesive agentcontaining various polyols (the above-mentioned adhesive componentshaving a hydroxy group) and a polyisocyanate. Further preferableexamples include a two-liquid curable polyurethane adhesive agentcontaining, as a main agent, a polyol such as polyester polyol,polyether polyol, or acrylic polyol and containing, as the curing agent,an aromatic or aliphatic polyisocyanate.

The thickness of the adhesive agent layer 2 is not particularly limitedas long as it exhibits a function as an adhesive layer. The thickness ofthe adhesive agent layer 2 is, for example, about 1 to 10 μm, preferablyabout 2 to 5 μm.

[Barrier Layer 3]

In the battery packaging material, the barrier layer 3 is a layer thathas a function of preventing ingress of, for example, water vapor,oxygen, and light into a battery, in addition to improving the strengthof the battery packaging material. The barrier layer 3 is preferably ametal layer, i.e., a layer formed of metal. Specific examples of themetal that forms the barrier layer 3 include aluminum, stainless steel,and titanium. Aluminum is preferred, for example. The barrier layer 3can be formed of, for example, a metal foil, a metal deposition film, aninorganic oxide deposition film, a carbon-containing inorganic oxidedeposition film, or a film provided with these deposition films. Thebarrier layer 3 is preferably formed of a metal foil, further preferablyformed of an aluminum alloy foil. The barrier layer 3 is more preferablyformed of a soft aluminum alloy foil such as annealed aluminum (JISH4160: 1994 A8021H-O, JIS H4160: 1994 A8079H-O, JIS H4000: 2014A8021P-O, JIS H4000: 2014 A8079P-O), from a viewpoint of preventinggeneration of wrinkles and pinholes on the barrier layer 3 duringproduction of the battery packaging material.

The thickness of the barrier layer 3 is not particularly limited as longas it exhibits a barrier function against, for example, water vapor. Thethickness of the barrier layer 3 is, for example, preferably about 100μm or less, more preferably about 10 to 100 μm, further preferably about10 to 80 μm, from a viewpoint of reducing the thickness of the batterypackaging material.

At least one surface, preferably both surfaces of the barrier layer 3are preferably subjected to a chemical conversion treatment for, forexample, stabilizing the adhesion and preventing dissolution andcorrosion. Here, the chemical conversion treatment is a treatment forforming an acid resistance film on a surface of the barrier layer. Inthe present invention, the barrier layer 3 may include the acidresistance film on one surface or both surfaces thereof or may includeno acid resistance film. Examples of the chemical conversion treatmentinclude a chromate treatment using a chromium compound such as chromiumnitrate, chromium fluoride, chromium sulfate, chromium acetate, chromiumoxalate, chromium biphosphate, acetylacetate chromate, chromiumchloride, or chromium potassium sulfate; a phosphoric acid treatmentusing a phosphoric acid compound such as sodium phosphate, potassiumphosphate, ammonium phosphate, or polyphosphoric acid; and a chromatetreatment using an aminated phenolic polymer having a repeating unit(s)represented by the following general formulae (1) to (4). In theaminated phenolic polymer, the repeating units represented by thegeneral formulae (1) to (4) may be contained alone or in any combinationof two or more thereof.

In the general formulae (1) to (4), X represents a hydrogen atom, ahydroxyl group, an alkyl group, a hydroxyalkyl group, an allyl group, ora benzyl group. R¹ and R² are identical or different, and each representa hydroxyl group, an alkyl group, or a hydroxyalkyl group. In thegeneral formulae (1) to (4), examples of the alkyl group represented byX, R¹ and R² include a linear or branched alkyl group with 1 to 4 carbonatoms, such as a methyl group, an ethyl group, a n-propyl group, anisopropyl group, a n-butyl group, an isobutyl group, and a tert-butylgroup. Examples of the hydroxyalkyl group represented by X, R¹, and R²include a linear or branched alkyl group that is substituted with onehydroxy group and has 1 to 4 carbon atoms, such as a hydroxymethylgroup, a 1-hydroxyethyl group, a 2-hydroxyethyl group, a 1-hydroxypropylgroup, a 2-hydroxypropyl group, a 3-hydroxypropyl group, a1-hydroxybutyl group, a 2-hydroxybutyl group, a 3-hydroxybutyl group,and a 4-hydroxybutyl group. In the general formulae (1) to (4), thealkyl groups and the hydroxyalkyl groups represented by X, R¹, and R²may be identical or different. In the general formulae (1) to (4), X ispreferably a hydrogen atom, a hydroxyl group, or a hydroxyalkyl group.The number average molecular weight of the aminated phenolic polymerhaving a repeating unit(s) represented by the general formulae (1) to(4) is, for example, preferably about 500 to about 1000000, morepreferably about 1000 to about 20000.

Examples of a chemical conversion treatment method for impartingcorrosion resistance to the barrier layer 3 include a method for coatingthe barrier layer 3 with a dispersion of fine particles of a metal oxidesuch as aluminum oxide, titanium oxide, cerium oxide, or tin oxide, orbarium sulfate in phosphoric acid, and baking the barrier layer 3 at150° C. or higher to form the acid resistance film on a surface of thebarrier layer 3. A resin layer obtained by crosslinking a cationicpolymer with a crosslinking agent may be further formed on the acidresistance film. Here, examples of the cationic polymer includepolyethyleneimine, an ion polymer complex formed of a polymer havingpolyethyleneimine and a carboxylic acid, a primary amine-grafted acrylicresin obtained by graft-polymerizing a primary amine with an acrylicmain backbone, polyallylamine or derivatives thereof, and anaminophenol. These cationic polymers may be used alone or in combinationof two or more thereof. Examples of the crosslinking agent include acompound having at least one functional group selected from the groupconsisting of an isocyanate group, a glycidyl group, a carboxyl group,and an oxazoline group, and a silane coupling agent. These crosslinkingagents may be used alone or in combination of two or more thereof.

A method for specifically providing the acid resistance film is, forexample, a method for first degreasing at least an inner-layer sidesurface of an aluminum alloy foil by a known treatment method such as analkali immersion method, an electrolytic cleaning method, an acidcleaning method, an electrolytic acid cleaning method, or an acidactivation method, and then coating the degreased surface with atreatment solution (aqueous solution) containing, as a main component,metal phosphate salts such as chromium phosphate salt, titaniumphosphate salt, zirconium phosphate salt, and zinc phosphate salt and amixed product of these metal salts, with a treatment solution (aqueoussolution) containing, as a main component, nonmetal phosphate salts anda mixed product of these nonmetal salts, or with a treatment solution(aqueous solution) containing a mixture of these metal phosphate saltsand/or nonmetal phosphate salts with an aqueous synthetic resin such asan acrylic resin, a phenolic resin, or a urethane resin, by a knowncoating method such as roll coating, gravure printing, or an immersionmethod. Thus, it is possible to form the acid resistance film. Forexample, a treatment with a chromium phosphate salt-based treatmentsolution forms an acid resistance film made of chromium phosphate,aluminum phosphate, aluminum oxide, aluminum hydroxide, aluminumfluoride, or the like, and a treatment with a zinc phosphate salt-basedtreatment solution forms an acid resistance film made of zinc phosphatehydrate, aluminum phosphate, aluminum oxide, aluminum hydroxide,aluminum fluoride, or the like.

Another example of the specific method for providing the acid resistancefilm is, for example, a method for first degreasing at least aninner-layer side surface of an aluminum alloy foil by a known treatmentmethod such as an alkali immersion method, an electrolytic cleaningmethod, an acid cleaning method, an electrolytic acid cleaning method,or an acid activation method, and then subjecting the degreased surfaceto a known anodization treatment. Thus, it is possible to form the acidresistance film.

Other examples of the acid resistance film include a phosphatesalt-based film and a chromic acid-based film. Examples of the phosphatesalt-based film include a zinc phosphate film, an iron phosphate film, amanganese phosphate film, a calcium phosphate film, and a chromiumphosphate film. Examples of the chromic acid-based film include achromium chromate film.

As another example of the acid resistance film, the acid resistance filmis formed of, for example, a phosphate salt, a chromate salt, fluoride,or a triazine thiol compound to exhibit an effect of preventingdelamination between aluminum and a layer functioning as the basematerial layer during emboss molding, preventing dissolution andcorrosion of a surface of aluminum, particularly dissolution andcorrosion of aluminum oxide existing on a surface of aluminum that arecaused by hydrogen fluoride generated through a reaction of anelectrolyte with moisture, improving the adhesiveness (wettability) on asurface of aluminum, preventing delamination between a layer functioningas the base material and aluminum during heat sealing, and preventing,for embossed aluminum, delamination between a layer functioning as thebase material layer and aluminum during press molding. Among thesubstances for forming the acid resistance film, good for application toa surface of aluminum and bake drying is an aqueous solution formed ofthree components, i.e., a phenolic resin, a chromium (III) fluoridecompound, and phosphoric acid.

The acid resistance film includes a layer containing cerium oxide,phosphoric acid or a phosphate salt, an anionic polymer, and acrosslinking agent for crosslinking the anionic polymer, and thephosphoric acid or the phosphate salt may be blended in an amount ofabout 1 to 100 parts by mass relative to 100 parts by mass of the ceriumoxide. The acid resistance film preferably has a multilayer structurefurther including a layer that contains a cationic polymer and acrosslinking agent for crosslinking the cationic polymer.

The anionic polymer is preferably a copolymer containing, as a maincomponent, poly(meth)acrylic acid or a salt thereof, or (meth)acrylicacid or a salt thereof. The crosslinking agent is preferably at leastone selected from the group consisting of a compound having any onefunctional group of an isocyanate group, a glycidyl group, a carboxylgroup, and an oxazoline group, and a silane coupling agent.

The phosphoric acid or the phosphate salt is preferably condensedphosphoric acid or a condensed phosphate salt.

As for the chemical conversion treatment, only one chemical conversiontreatment may be performed, or two or more chemical conversiontreatments may be performed in combination. These chemical conversiontreatments may be performed using one compound alone or two or morecompounds in combination. Among the chemical conversion treatments,preferred are, for example, a chromate treatment and a chemicalconversion treatment using a chromium compound, a phosphoric acidcompound, and an aminated phenolic polymer in combination. Particularly,the chromium compound is preferably a chromic acid compound.

Specific examples of the acid resistance film include a film containingat least one of a phosphate salt, a chromate salt, fluoride, or triazinethiol. An acid resistance film containing a cerium compound is alsopreferred. The cerium compound is preferably cerium oxide.

Specific examples of the acid resistance film also include a phosphatesalt-based film, a chromate salt-based film, a fluoride-based film, anda triazine thiol compound film. The acid resistance film may be one ofthese films or a combination of a plurality of films. Further, the acidresistance film may be a film formed with a treatment solutioncontaining a mixture of a metal phosphate salt with an aqueous syntheticresin or a treatment solution containing a mixture of a nonmetalphosphate salt with an aqueous synthetic resin, after degreasing asurface of an aluminum alloy foil to be subjected to a chemicalconversion treatment.

The composition of the acid resistance film can be analyzed accordingto, for example, time-of-flight secondary ion mass spectrometry. Theanalysis of the composition of the acid resistance film according totime-of-flight secondary ion mass spectrometry allows detection of, forexample, a peak(s) derived from at least one of Ce⁺ or Cr⁺.

A surface of the aluminum alloy foil preferably includes the acidresistance film containing at least one element selected from the groupconsisting of phosphorus, chromium, and cerium. It is possible toconfirm by X-ray photoemission spectroscopy that the acid resistancefilm on the surface of the aluminum alloy foil in the battery packagingmaterial contains at least one element selected from the groupconsisting of phosphorus, chromium, and cerium. Specifically, first, theheat-sealable resin layer, the adhesive agent layer, and the like arephysically delaminated that have been laminated on the aluminum alloyfoil in the battery packaging material. Next, the aluminum alloy foil isput in an electric furnace and an organic component existing on thesurface of the aluminum alloy foil is removed at about 300° C. for about30 minutes. Subsequently, the surface of the aluminum alloy foil isconfirmed by X-ray photoemission spectroscopy that the surface containsthe element(s).

The amount of the acid resistance film to be formed on the surface ofthe barrier layer 3 in the chemical conversion treatment is notparticularly limited, but, for example, when the above-mentionedchromate treatment is performed, it is desirable that the chromiccompound be contained in an amount of about 0.5 to 50 mg, preferablyabout 1.0 to 40 mg in terms of chromium, the phosphorus compound becontained in an amount of about 0.5 to 50 mg, preferably about 1.0 to 40mg in terms of phosphorus, and the aminated phenolic polymer becontained in an amount of about 1.0 to 200 mg, preferably about 5.0 to150 mg, per 1 m² of the surface of the barrier layer 3.

The thickness of the acid resistance film is not particularly limitedbut is, for example, preferably about 1 nm to about 10 μm, morepreferably about 1 to 100 nm, further preferably about 1 to 50 nm, froma viewpoint of cohesion force of the film and adhesion force between theacid resistance film and the barrier layer 3 or the heat-sealable resinlayer. The thickness of the acid resistance film can be measured byobservation with a transmission electron microscope or by a combinationof observation with a transmission electron microscope and energydispersive X-ray spectroscopy or electron energy-loss spectroscopy.

The chemical conversion treatment is performed by applying a solutioncontaining a compound used for forming the acid resistance film to asurface of the barrier layer through, for example, bar coating, rollcoating, gravure coating, or an immersion method, and then heating thebarrier layer such that the temperature of the barrier layer becomesabout 70 to 200° C. The barrier layer may be degreased by an alkaliimmersion method, an electrolytic cleaning method, an acid cleaningmethod, an electrolytic acid cleaning method or the like beforesubjected to a chemical conversion treatment. When degreasing isperformed as described above, the chemical conversion treatment on thesurface of the barrier layer can be more efficiently performed.

[Heat-Sealable Resin Layer 4]

In the battery packaging material according to the present invention,the heat-sealable resin layer 4 corresponds to an innermost layer and isa layer whose portions are heat-sealed to each other during assembly ofa battery to hermetically seal a battery element in the heat-sealableresin layer.

A resin component used for the heat-sealable resin layer 4 is notparticularly limited as long as it is heat-sealable, and examples of theresin component include a polyolefin, a cyclic polyolefin, a carboxylicacid-modified polyolefin, and a carboxylic acid-modified cyclicpolyolefin. That is, the resin that forms the heat-sealable resin layer4 may optionally have a polyolefin backbone but preferably has apolyolefin backbone. The polyolefin backbone contained in the resin thatforms the heat-sealable resin layer 4 can be confirmed by analysis suchas infrared spectroscopy or gas chromatography-mass spectrometry, andthe analysis method is not particularly restricted. For example,measurement of a maleic anhydride-modified polyolefin by infraredspectroscopy detects peaks derived from maleic anhydride at wave numbersof around 1760 cm⁻¹ and around 1780 cm⁻¹. When the degree of acidmodification is low, however, a peak becomes small to be sometimesundetected. In that case, analysis can be performed by nuclear magneticresonance spectroscopy.

Specific examples of the polyolefin include polyethylene such aslow-density polyethylene, medium-density polyethylene, high-densitypolyethylene, and linear low-density polyethylene; polypropylene such ashomopolypropylene, polypropylene as a block copolymer (e.g., a blockcopolymer of propylene and ethylene), and polypropylene as a randomcopolymer (e.g., a random copolymer of propylene and ethylene); and aterpolymer of ethylene-butene-propylene. Among these polyolefins,polyethylene and polypropylene are preferred.

The cyclic polyolefin is a copolymer of an olefin and a cyclic monomer,and examples of the olefin as a constituent monomer of the cyclicpolyolefin include ethylene, propylene, 4-methyl-1-pentene, butadiene,and isoprene. Examples of the cyclic monomer as a constituent monomer ofthe cyclic polyolefin include cyclic alkenes such as norbornene;specific examples include cyclic dienes such as cyclopentadiene,dicyclopentadiene, cyclohexadiene, and norbornadiene. Among thesepolyolefins, cyclic alkenes are preferred, and norbornene is furtherpreferred, for example. It is also possible to use styrene as aconstituent monomer.

The carboxylic acid-modified polyolefin is a polymer obtained bymodifying the polyolefin with a carboxylic acid through blockpolymerization or graft polymerization. Examples of the carboxylic acidused for the modification include maleic acid, acrylic acid, itaconicacid, crotonic acid, maleic anhydride, and itaconic anhydride.

The carboxylic acid-modified cyclic polyolefin is a polymer obtained bycopolymerizing a part of a monomer that constitutes the cyclicpolyolefin with the α,β-unsaturated carboxylic acid or the anhydridethereof, or by block-polymerizing or graft-polymerizing the cyclicpolyolefin with an α,β-unsaturated carboxylic acid or an anhydridethereof. The cyclic polyolefin to be modified with a carboxylic acid isthe same as described above. The carboxylic acid used for themodification is the same as used for the modification of theacid-modified polyolefin.

Among these resin components, a carboxylic acid-modified polyolefin ispreferred; and carboxylic acid-modified polypropylene is furtherpreferred, for example.

The heat-sealable resin layer 4 may be formed of one resin componentalone or a blended polymer obtained by combining two or more resincomponents. Further, the heat-sealable resin layer 4 may be formed ofonly one layer or two or more layers with the identical resin componentor different resin components.

A lubricant may be contained in the heat-sealable resin layer 4. Thelubricant existing on a surface of the heat-sealable resin layer 4 maybe one oozed out from a lubricant contained in a resin that forms theheat-sealable resin layer 4, or one applied on a surface of theheat-sealable resin layer 4. The heat-sealable resin layer 4 containinga lubricant is capable of increasing the moldability of the batterypackaging material. The lubricant is not particularly limited and aknown lubricant may be used. Examples of the lubricant include thoseexemplified above for the polyester film 1. These lubricants may be usedalone or in combination of two or more thereof. The abundance of thelubricant on the surface of the heat-sealable resin layer 4 is notparticularly limited but is, for example, preferably about 10 to 50mg/m², further preferably about 15 to 40 mg/m² in an environment at atemperature of 24° C. and a relative humidity of 60%, from a viewpointof increasing the moldability of the electron packaging material.

As described above, in recent years, the battery packaging material isbeing required to be furthermore reduced in film thickness, along with arequirement of reducing the size and the thickness of batteries.Therefore, the thickness of the heat-sealable resin layer situated as aninnermost layer of the battery packaging material is also required to bedecreased to the minimum possible thickness. However, when the ratio ofthe thickness of the heat-sealable resin layer to the thickness of thebase material decreases, a peripheral edge of a concave portion formedon the battery packaging material is curled (curved), so that storage ofa battery element and heat sealing of the heat-sealable resin layer maybe hindered, leading to deterioration of production efficiency ofbatteries. Particularly, a battery packaging material to be used in alarge secondary battery such as a secondary battery for use in cars hasa problem that since the battery packaging material has a large size,the impact of curling on productivity of batteries is very large.

When the ratio of the thickness of the heat-sealable resin layer 4 tothe thickness of the polyester film 1 decreases (for example, the ratioof the thickness of the heat-sealable resin layer 4 to the thickness ofthe polyester film 1 (thickness of heat-sealable resin layer/thicknessof polyester film) is 4 or less, with the thickness of the polyesterfilm 1 defined as 1), the battery packaging material is likely toincrease the size of curling after molding. The battery packagingmaterial according to the present invention, however, has a degree ofsurface orientation (Y_(ma)/Y_(min)) in the range of 1.4 to 2.7, so thatthe battery packaging material has excellent moldability and effectivelyminimizes curling after molding. In the battery packaging materialaccording to the present invention, the ratio of the thickness of theheat-sealable resin layer 4 to the thickness of the polyester film 1(thickness of heat-sealable resin layer/thickness of polyester film) is4 or less as a preferable upper limit, less than 3 as more preferableupper limit, 2 or less as further preferable upper limit and is, forexample, 1 or more as a preferable lower limit, from a viewpoint ofsuitably minimizing curling after molding. The ratio is preferably in arange of 1 or more and 4 or less, more preferably in a range of 1 ormore and less than 3, further preferably in a range of 1 or more and 2or less.

The thickness of the heat-sealable resin layer 4 is, for example,preferably about 100 μm or less, more preferably about 40 μm or less asan upper limit and is, for example, about 15 μm or more as a lowerlimit, from a viewpoint of reducing the thickness of the batterypackaging material to the minimum possible and minimizing curling aftermolding. The thickness of the heat-sealable resin layer 4 is preferablyin a preferable range of about 15 to 100 μm, more preferably in a rangeof about 15 to 40 μm.

[Adhesive Layer 5]

In the battery packaging material according to the present invention,the adhesive layer 5 is a layer provided between the barrier layer 3 andthe heat-sealable resin layer 4 as necessary, for strongly bonding theselayers to each other.

The adhesive layer 5 is formed of a resin capable of bonding the barrierlayer 3 to the heat-sealable resin layer 4. As the resin used forforming the adhesive layer 5, it is possible to use, for example, thesame adhesive agents as exemplified for the adhesive agent layer 2 interms of the bonding mechanism of the resin, the type of an adhesiveagent component, and the like. As the resin used for forming theadhesive layer 5, it is also possible to use polyolefin-based resinsexemplified above for the heat-sealable resin layer 4, such as apolyolefin, a cyclic polyolefin, a carboxylic acid-modified polyolefin,and a carboxylic acid-modified cyclic polyolefin. That is, the resinthat forms the adhesive layer 5 may optionally have a polyolefinbackbone but preferably has a polyolefin backbone. The polyolefinbackbone contained in the resin that forms the adhesive layer 5 can beconfirmed by analysis such as infrared spectroscopy or gaschromatography-mass spectrometry, and the analysis method is notparticularly restricted. For example, measurement of a maleicanhydride-modified polyolefin by infrared spectroscopy detects peaksderived from maleic anhydride at wave numbers of around 1760 cm⁻¹ andaround 1780 cm⁻¹. When the degree of acid modification is low, however,a peak becomes small to be sometimes undetected. In that case, analysiscan be performed by nuclear magnetic resonance spectroscopy. Thepolyolefin is preferably a carboxylic acid-modified polyolefin,particularly preferably a carboxylic acid-modified polypropylene,because they are excellent in adhesion between the barrier layer 3 andthe heat-sealable resin layer 4.

Further, the adhesive layer 5 may be a cured product of a resincomposition containing an acid-modified polyolefin and a curing agent,from a viewpoint of reducing the thickness of the battery packagingmaterial and providing the battery packaging material excellent in shapestability after molding. As the acid-modified polyolefin, there can beexemplified the same carboxylic acid-modified polyolefin and carboxylicacid-modified cyclic polyolefin as exemplified for the heat-sealableresin layer 4. The adhesive layer 5 is preferably a cured product of aresin composition containing at least one selected from the groupconsisting of an isocyanate group-containing compound, an oxazolinegroup-containing compound, and an epoxy group-containing compound. Theadhesive layer 5 is particularly preferably a cured product of a resincomposition containing at least one selected from the group consistingof an isocyanate group-containing compound and an epoxy group-containingcompound. The adhesive layer 5 preferably contains at least one selectedfrom the group consisting of a urethane resin, an amide ester resin, andan epoxy resin. The adhesive layer 5 more preferably contains a urethaneresin and an epoxy resin. The adhesive layer 5 is more preferably acured product of a resin composition containing at least one of thesecompounds and resins, and the above-mentioned acid-modified polyolefin.When in the adhesive layer 5 is left an unreacted product of a curingagent such as an isocyanate group-containing compound, an oxazolinegroup-containing compound, or an epoxy resin, it is possible to confirmthe existence of the unreacted product by a method selected from, forexample, infrared spectroscopy, Raman spectroscopy, and time-of-flightsecondary ion mass spectrometry (TOF-SIMS).

The curing agent is not particularly limited as long as it cures theacid-modified polyolefin. Examples of the curing agent include anepoxy-based curing agent, a polyfunctional isocyanate-based curingagent, a carbodiimide-based curing agent, and an oxazoline-based curingagent. The adhesive layer 5 is preferably a cured product of a resincomposition containing a curing agent having at least one selected fromthe group consisting of an oxygen atom, a heterocyclic ring, a C═N bond,and a C—O—C bond, from a viewpoint of further increasing the adhesionbetween the acid resistance film and the adhesive layer 5. Examples ofthe curing agent having a heterocyclic ring include an oxazolinegroup-containing curing agent and an epoxy group-containing curingagent. Examples of the curing agent having a C═N bond include anoxazoline group-containing curing agent and an isocyanategroup-containing curing agent. Examples of the curing agent having aC—O—C bond include an oxazoline group-containing curing agent, an epoxygroup-containing curing agent, and a urethane resin. The fact that theadhesive layer 5 is a cured product of a resin composition containingthese curing agents can be confirmed by a method such as gaschromatography-mass spectrometry (GCMS), infrared spectroscopy (IR),time-of-flight secondary ion mass spectrometry (TOF-SIMS), or X-rayphotoemission spectroscopy (XPS).

The epoxy-based curing agent is not particularly limited as long as itis a compound having at least one epoxy group. Examples of theepoxy-based curing agent include epoxy resins such as bisphenol Adiglycidyl ether, modified bisphenol A diglycidyl ether, novolakglycidyl ether, glycerin polyglycidyl ether, and polyglycerinpolyglycidyl ether.

The polyfunctional isocyanate-based curing agent is not particularlylimited as long as it is a compound having two or more isocyanategroups. Specific examples of the polyfunctional isocyanate-based curingagent include isophorone diisocyanate (IPDI), hexamethylene diisocyanate(HDI), tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI),polymerized or nurated products thereof, mixtures thereof, andcopolymerized products thereof with another polymer.

The carbodiimide-based curing agent is not particularly limited as longas it is a compound having at least one carbodiimide group (—N═C═N—).The carbodiimide-based curing agent is preferably a polycarbodiimidecompound having at least two carbodiimide groups.

The oxazoline-based curing agent is not particularly limited as long asit is a compound having an oxazoline backbone. Specific examples of theoxazoline-based curing agent include EPOCROS Series manufactured byNIPPON SHOKUBAI CO., LTD.

The curing agent may be formed of two or more compounds from a viewpointof increasing the adhesion between the barrier layer 3 and theheat-sealable resin layer 4 by the adhesive layer 5.

The content of the curing agent in the resin composition for forming theadhesive layer 5 is preferably in a range of 0.1 to 50% by mass, morepreferably in a range of 0.1 to 30% by mass, further preferably in arange of 0.1 to 10% by mass.

The thickness of the adhesive layer 5 is not particularly limited aslong as it exhibits a function as an adhesive layer. When an adhesiveagent exemplified for the adhesive agent layer 2 is used, however, thethickness of the adhesive layer 5 is, for example, preferably about 2 to10 μm, more preferably about 2 to 5 μm. When a resin exemplified for theheat-sealable resin layer 4 is used, the thickness of the adhesive layer5 is, for example, preferably about 2 to 50 μm, more preferably about 10to 40 μm. When the adhesive layer 5 is a cured product of anacid-modified polyolefin and a curing agent, the thickness of theadhesive layer 5 is, for example, preferably about 30 μm or less, morepreferably about 0.1 to 20 μm, further preferably about 0.5 to 5 μm.When the adhesive layer 5 is a cured product of a resin compositioncontaining an acid-modified polyolefin and a curing agent, it ispossible to form the adhesive layer 5 by application of the resincomposition followed by, for example, heating for curing.

[Surface Coating Layer 6]

In the battery packaging material according to the present invention,the surface coating layer 6 may be provided on the polyester film 1 (apolyester film 1's surface opposite to the barrier layer 3) asnecessary, for the purpose of, for example, improving designability,electrolytic solution resistance, scratch resistance, and moldability.The surface coating layer 6 is a layer situated as an outermost layerwhen a battery is assembled.

The surface coating layer 6 can be formed of, for example,polyvinylidene chloride, a polyester resin, a urethane resin, an acrylicresin, or an epoxy resin. Among these resins, the surface coating layer6 is preferably formed of a two-liquid curable resin. Examples of thetwo-liquid curable resin for forming the surface coating layer 6 includea two-liquid curable urethane resin, a two-liquid curable polyesterresin, and a two-liquid curable epoxy resin. The surface coating layer 6may also contain an additive.

Examples of the additive include fine particles having a particle sizeof 0.5 nm to 5 μm. A material for the additive is not particularlylimited, and examples of the material include a metal, a metal oxide, aninorganic substance, and an organic substance. A shape of the additiveis not also particularly limited, and examples of the shape include aspherical shape, a fibrous shape, a plate shape, an amorphous shape, anda balloon shape. Specific examples of the additive include talc, silica,graphite, kaolin, montmorilloide, montmorillonite, synthetic mica,hydrotalcite, silica gel, zeolite, aluminum hydroxide, magnesiumhydroxide, zinc oxide, magnesium oxide, aluminum oxide, neodymium oxide,antimony oxide, titanium oxide, cerium oxide, calcium sulfate, bariumsulfate, calcium carbonate, calcium silicate, lithium carbonate, calciumbenzoate, calcium oxalate, magnesium stearate, alumina, carbon black,carbon nanotubes, high-melting-point nylon, crosslinked acrylic,crosslinked styrene, crosslinked polyethylene, benzoguanamine, gold,aluminum, copper, and nickel. These additives may be used alone or incombination of two or more thereof. Among these additives, preferredare, for example, silica, barium sulfate, and titanium oxide from aviewpoint of, for example, dispersion stability, and costs. The additivemay have the surface thereof subjected to various surface treatmentssuch as an insulation treatment and a dispersibility enhancingtreatment.

The content of the additive in the surface coating layer 6 is notparticularly limited but is, for example, preferably about 0.05 to 1.0%by mass, more preferably about 0.1 to 0.5% by mass.

A method for forming the surface coating layer 6 is not particularlylimited, and examples of the method include a method for applying atwo-liquid curable resin for forming the surface coating layer 6 ontoone surface of the polyester film 1. When the additive is blended,application may be performed after the additive is added to and mixedwith the two-liquid curable resin.

The thickness of the surface coating layer 6 is not particularly limitedas long as it exhibits the above-mentioned functions as the surfacecoating layer 6. The thickness of the surface coating layer 6 is, forexample, 0.5 to 10 μm, preferably 1 to 5 μm.

3. Method for Producing Battery Packaging Material

A method for producing a battery packaging material according to thepresent invention is not particularly limited as long as it is capableof giving a laminate including layers that each have predeterminedcomposition and are laminated on top of another. The method forproducing a battery packaging material is, for example, a methodincluding: a step of obtaining a laminate by laminating at least apolyester film, a barrier layer, and a heat-sealable resin layer in thisorder; and using, as the polyester film, a polyester film having a ratioin a range of 1.4 to 2.7 between a maximum value Y_(max) and a minimumvalue Y_(min) (degree of surface orientation: Y_(max)/Y_(min)), with themaximum value Y_(max) and the minimum value Y_(min) respectivelyrepresenting a maximum value and a minimum value of a ratio between anabsorption peak intensity Y₁₃₄₀ at 1340 cm⁻¹ and an absorption peakintensity Y₁₄₁₀ at 1410 cm⁻¹ (Y₁₃₄₀/Y₁₄₁₀) in infrared absorptionspectra acquired for 18 directions at intervals of 10° from 00 to 1800on a surface of the polyester film according to attenuated totalreflection of Fourier transform infrared spectroscopy.

One example of the method for producing a battery packaging materialaccording to the present invention is as follows. First, a laminate isformed that includes a polyester film 1, an adhesive agent layer 2, anda barrier layer 3 laminated in this order (hereinafter, the laminate maybe described as a “laminate A”). Specifically, the laminate A can beformed according to a dry lamination method for applying, by a coatingmethod such as gravure coating or roll coating, an adhesive agent usedfor forming the adhesive agent layer 2 onto the polyester film 1 or thebarrier layer 3 having a surface thereof subjected to a chemicalconversion treatment as necessary, drying the adhesive agent, thenlaminating the barrier layer 3 or the polyester film 1 on top of theother, and curing the adhesive agent layer 2.

Next, an adhesive layer 5 and a heat-sealable resin layer 4 arelaminated in this order on the barrier layer 3 of the laminate A. Therecan be exemplified (1) a method for laminating, through coextrusion, theadhesive layer 5 and the heat-sealable resin layer 4 on the barrierlayer 3 of the laminate A (coextrusion lamination method); (2) a methodfor separately forming a laminate including the adhesive layer 5 and theheat-sealable resin layer 4 laminated on top of another and laminatingthis laminate on the barrier layer 3 of the laminate A by a thermallamination method; (3) a method for applying an adhesive agent forformation of the adhesive layer 5 onto the barrier layer 3 of thelaminate A by an extrusion method or solution coating and subjecting theadhesive agent to, for example, drying at high temperature and furtherbaking to laminate the adhesive layer 5 on the barrier layer 3, andlaminating the heat-sealable resin layer 4, which has been formed in asheet shape beforehand, on this adhesive layer 5 by a thermal laminationmethod; and (4) a method for pouring the adhesive layer 5, which hasbeen melted, into between the barrier layer 3 of the laminate A and theheat-sealable resin layer 4 that has been formed in a sheet shapebeforehand and simultaneously sticking the laminate A to theheat-sealable resin layer 4 with the adhesive layer 5 interposedtherebetween (sandwich lamination method).

When a surface coating layer 6 is provided, the surface coating layer 6is laminated on a polyester film 1's surface opposite to the barrierlayer 3. The surface coating layer 6 can be formed by, for example,applying the above-mentioned resin for forming the surface coating layer6 to the surface of the polyester film 1. The order is not particularlylimited for a step of laminating the barrier layer 3 on a surface of thepolyester film 1 and a step of laminating the surface coating layer 6 ona surface of the polyester film 1. For example, after the surfacecoating layer 6 is formed on a surface of the polyester film 1, thebarrier layer 3 may be formed on the polyester film 1's surface oppositeto the surface coating layer 6.

As described above, a laminate is formed that includes the surfacecoating layer 6 provided as necessary, the polyester film 1, theadhesive agent layer 2 provided as necessary, the barrier layer 3 havingthe surface thereof subjected to a chemical conversion treatment asnecessary, the adhesive layer 5, and the heat-sealable resin layer 4.The laminate may be further subjected to a hot roll contact-type, hotair-type, or near- or far-infrared-type heating treatment, in order tostrengthen the adhesiveness of the adhesive agent layer 2 or theadhesive layer 5. As the conditions for such a heating treatment, therecan be exemplified heating at about 150 to 250° C. for about 1 to 5minutes.

In the battery packaging material according to the present invention,the layers that form the laminate may be subjected to a surfaceactivation treatment such as a corona treatment, a blast treatment, anoxidation treatment, or an ozone treatment as necessary, in order toimprove or stabilize, for example, film formability, laminationprocessing, and final product secondary processing (pouching andembossing molding) suitability.

4. Use of Battery Packaging Material

The battery packaging material according to the present invention isused as packaging for hermetically sealing and storing a battery elementsuch as a positive electrode, a negative electrode, and an electrolytetherein. That is, a battery element including at least a positiveelectrode, a negative electrode, and an electrolyte can be stored inpackaging formed of the battery packaging material according to thepresent invention to form a battery.

Specifically, a battery element including at least a positive electrode,a negative electrode, and an electrolyte is covered with the batterypackaging material according to the present invention such that a flangepart (region where portions of a heat-sealable resin layer are incontact with each other) can be formed on a periphery of the batteryelement, while metal terminals connected to the positive electrode andthe negative electrode respectively are allowed to extrude exteriorly,and the portions of the heat-sealable resin layer at the flange part arehermetically heat-sealed to each other, thereby providing a batteryproduced by using the battery packaging material. When a battery elementis stored in packaging formed of the battery packaging materialaccording to the present invention, the packaging is formed such that aheat-sealable resin portion of the battery packaging material accordingto the present invention comes inside (surface in contact with thebattery element).

The battery packaging material according to the present invention may beused for either a primary battery or a secondary battery but ispreferably used for a secondary battery. The type of the secondarybattery to which the battery packaging material according to the presentinvention is applied is not particularly limited, and examples of thesecondary battery include a lithium ion battery, a lithium ion polymerbattery, a lead storage battery, a nickel-hydrogen storage battery, anickel-cadmium storage battery, a nickel-iron storage battery, anickel-zinc storage battery, a silver oxide-zinc storage battery, ametal-air battery, a polyvalent cation battery, a condenser, and acapacitor. Among these secondary batteries, for example, a lithium ionbattery and a lithium ion polymer battery are suitable subjects forapplication of the battery packaging material according to the presentinvention.

5. Polyester Film

A polyester film according to the present invention is a polyester filmused for use in a battery packaging material. The polyester filmaccording to the present invention is characterized by having a ratio ina range of 1.4 or more and 2.7 or less between a maximum value Y_(max)and a minimum value Y_(min) (degree of surface orientation:Y_(max)/Y_(min)), with the maximum value Y_(max) and the minimum valueY_(min) respectively representing a maximum value and a minimum value ofa ratio between an absorption peak intensity Y₁₃₄₀ at 1340 cm⁻¹ and anabsorption peak intensity Y₁₄₁₀ at 1410 cm⁻¹ (Y₁₃₄₀/Y₁₄₁₀) in infraredabsorption spectra acquired for 18 directions at intervals of 10° from0° to 180° on a surface of the polyester film according to attenuatedtotal reflection of Fourier transform infrared spectroscopy. Thespecific structure of the polyester film according to the presentinvention is the same structure as described in Section “2. LayersForming Battery Packaging Material [Polyester film 1].”

EXAMPLES

The present invention is described in detail below by way of examplesand comparative examples. It is to be noted that the present inventionis not limited to the examples.

Examples 1 to 7 and Comparative Examples 1 to 3 <Production of BatteryPackaging Material>

In each of the examples and the comparative examples, a barrier layerformed of an aluminum foil (JIS H4160: 1994 A8021H-O) was laminated on astretched polyethylene terephthalate film by a dry lamination method,the aluminum foil having both surfaces thereof subjected to a chemicalconversion treatment to form acid resistance films. Specifically, atwo-liquid curable urethane adhesive agent (a polyol compound and anaromatic isocyanate-based compound) was applied to one surface of thealuminum foil to form an adhesive agent layer (thickness: 3 μm) on thebarrier layer. Next, the adhesive agent layer on the barrier layer andthe polyethylene terephthalate film were laminated on top of another andsubjected to an aging treatment to prepare a laminate including thestretched polyethylene terephthalate film, the adhesive agent layer, andthe barrier layer. The chemical conversion treatment for the aluminumfoil used as the barrier layer was performed by applying to bothsurfaces of the aluminum foil a treatment solution containing a phenolicresin, a chromium fluoride compound, and phosphoric acid through rollcoating such that the application amount of chromium was 10 mg/m² (drymass), and baking the aluminum foil.

Next, maleic anhydride-modified polypropylene as an adhesive layer andrandom polypropylene as a heat-sealable resin layer were coextruded onthe barrier layer of the resultant laminate to laminate the adhesivelayer and the heat-sealable resin layer on the barrier layer. Next, theresultant laminate was subjected to aging and heating to give a batterypackaging material including the stretched polyethylene terephthalatefilm, the adhesive agent layer, the barrier layer, the adhesive layer,and the heat-sealable resin layer laminated in this order. The layerstructure and the thickness of the layers of the battery packagingmaterial are as shown in Table 1.

TABLE 1 Layer structure Example 1 PET(25)/DL(3)/ALM(35)/PPa(30)/PP(30)Example 2 PET(25)/DL(3)/ALM(35)/PPa(30)/PP(30) Example 3PET(25)/DL(3)/ALM(35)/PPa(30)/PP(30) Example 4PET(25)/DL(3)/ALM(35)/PPa(30)/PP(30) Comparative Example 1PET(25)/DL(3)/ALM(35)/PPa(30)/PP(30) Comparative Example 2PET(25)/DL(3)/ALM(35)/PPa(30)/PP(30) Example 5PET(12)/DL(3)/ALM(30)/PPa(14)/PP(10) Example 6PET(12)/DL(3)/ALM(30)/PPa(14)/PP(10) Example 7PET(12)/DL(3)/ALM(30)/PPa(14)/PP(10) Comparative Example 3PET(12)/DL(3)/ALM(30)/PPa(14)/PP(10)

In Table 1, a numerical value in parentheses of the layer structureindicates the thickness (μm).

<Measurement of Degree of Surface Orientation>

For each of a surface of the stretched polyester film laminated in thebattery packaging material and a surface of the stretched polyester filmas a single layer used for lamination, a ratio was calculated between amaximum value Y_(max) and a minimum value Y_(min) (degree of surfaceorientation: Y_(max)/Y_(min)), with the maximum value Y_(max) and theminimum value Y_(min) respectively representing a maximum value and aminimum value of a ratio between an absorption peak intensity Y₁₃₄₀ at1340 cm⁻¹ (CH₂ wagging vibration) and an absorption peak intensity Y₁₄₁₀at 1410 cm⁻¹ (C═C stretching vibration) (Y₁₃₄₀/Y₁₄₁₀) in infraredabsorption spectra acquired for 18 directions at intervals of 10° from0° to 180° on the surface of each of the stretched polyester filmsaccording to attenuated total reflection (ATR) of Fourier transforminfrared spectroscopy (FT-IR). Specific conditions for measuring theinfrared absorption spectra are as follows. Table 2 shows the results.

(Conditions for Measuring Infrared Absorption Spectra)

Spectrometer: Nicolet iS10 FT-IR manufactured by Thermo FisherScientific Inc.Attachment: attachment (Seagull) for single reflection ATR

Detector: MCT (Hg Cd Te)

Wavenumber resolution: 8 cm-1

IRE: Ge

Angle of incidence: 30°Polarizer: wire grid, S polarizationBaseline: average value of intensity in a wavenumber range of 1800 cm-1to 2000 cm-1Absorption peak intensity Y₁₃₄₀: value obtained by deducting value ofbaseline from maximum value of peak intensity in wavenumber range of1335 cm-1 to 1342 cm-1Absorption peak intensity Y₁₄₁₀: value obtained by deducting value ofbaseline from maximum value of peak intensity in wavenumber range of1400 cm-1 to 1410 cm-1

<Measurement of Birefringence Index>

A birefringence index of the polyethylene terephthalate film wasmeasured using a phase difference measuring apparatus (KOBRA-WRmanufactured by Oji Scientific Instruments Co., Ltd.). The measurementwavelength was set to 550 nm and the angle of incidence was set to 10degrees. The thickness of the polyethylene terephthalate film used forcalculating the birefringence index is a value measured using amicrometer (Digimatic Micrometer manufactured by Mitutoyo Corporation).An average refractive index of the polyester film used for calculationof the birefringence index was set to an assumed value of 1.6200. Table2 shows the results.

<Evaluation of Moldability>

Each of the battery packaging materials obtained above was cut into arectangle with length (z direction) 150 mm and width (x direction) 100mm to form a test sample. This sample was cold-molded (draw-in one-stepmolding) using a rectangular mold (female mold, surface: a maximumheight roughness (nominal value of Rz) of 3.2 μm that is specified inTable 2 of JIS B 0659-1: 2002, Annex 1 (reference), Standard SurfaceRoughness Piece for Comparison) having an opening size of 30 mm (xdirection)×50 mm (z direction) and a corresponding mold (male mold,surface: a maximum height roughness (nominal value of Rz) of 1.6 μm thatis specified in Table 2 of JIS B 0659-1: 2002, Annex 1 (reference),Standard Surface Roughness Piece for Comparison). The cold molding wasperformed while the molding depth was changed in 0.5-mm lengths from amolding depth of 0.5 mm at a pressing force (surface pressure) of 0.9MPa, and 10 samples were subjected to the cold molding at each depth. Atthis time, the molding was performed, with the test sample placed on thefemale mold such that the heat-sealable resin layer was situated on amale mold side. The male and female molds had a clearance of 0.5 mmtherebetween. As regards the samples cold-molded, a value calculated bythe following equation was defined as limited molding depth of thebattery packaging material, with A mm representing the deepest moldingdepth at which none of the 10 samples generated either pinholes orcracks on the aluminum foils, and B sample(s) representing the number ofsamples that generated pinholes or the like at the shallowest moldingdepth at which the aluminum foil generated pinholes or the like. Table 2shows the results.

Limited molding depth=A mm+(0.5 mm/10 samples)×(10 samples−B samples)

<Evaluation of Curling after Molding>

Each of the battery packaging materials obtained above was cut toprepare a strip piece with length (z direction) 150 mm and width (xdirection) 100 mm and the strip piece was used as a test sample. Next,the test sample was cold-molded (draw-in one-step molding) using themold used for evaluating the moldability, with the test sample placed onthe female mold such that the heat-sealable resin layer was situated ona male mold side, while the test sample was pressed at a pressingpressure (surface pressure) of 0.1 MPa to give a molding depth of 6 mm.FIG. 5 shows the details of a position at which molding was performed.As shown in FIG. 6, molding was performed at a position where a distanced was 75 mm between a rectangular molded part M and an end part P of abattery packaging material 10. Next, the battery packaging material 10molded was placed on a horizontal surface 20 as shown in FIG. 6, and amaximum value t of the distance along a vertical line y between thehorizontal surface 20 and the end part P was defined as the maximumheight (molding curling (mm)) of a curled portion. Table 2 shows theresults.

TABLE 2 Physical properties measured for PET film laminated in batterypackaging material Physical properties measured for PET film as singlelayer Degree of Degree of Curling surface surface Birefringence afterorientation orientation index Moldability molding Ymax Ymin Ymax/YminYmax Ymin Ymax/Ymin nx ny nx − ny (mm) (mm) Example 1 2.1 1.3 1.6 2.11.3 1.6 1.68833 1.66845 0.01988 6.2 25 Example 2 2.2 1.2 1.8 2.2 1.2 1.81.69776 1.67597 0.02179 6.1 25 Example 3 2.3 1.1 2.1 2.3 1.1 2.1 1.695481.67030 0.02518 6.2 23 Example 4 2.4 1.0 2.4 2.4 1.0 2.4 1.69168 1.650210.04147 6.1 20 Comparative 2.0 1.7 1.2 2.0 1.7 1.2 1.68404 1.669160.01488 6.0 50 Example 1 Comparative 2.8 1.0 2.8 2.8 1.0 2.8 1.693081.63677 0.05631 4.0 17 Example 2 Example 5 2.2 1.3 1.7 2.2 1.3 1.71.68737 1.66555 0.02182 4.5 24 Example 6 2.3 1.2 1.9 2.3 1.2 1.9 1.694711.66926 0.02545 4.4 20 Example 7 2.4 1.0 2.4 2.4 1.0 2.4 1.69142 1.649640.04178 4.2 17 Comparative 2.0 1.6 1.3 2.0 1.6 1.3 1.67156 1.656210.01535 4.5 38 Example 3

In Tables 1 and 2, PET represents the stretched polyethyleneterephthalate, DL represents the adhesive agent layer, ALM representsthe aluminum foil, PPa represents the adhesive layer formed of maleicanhydride-modified polypropylene, and PP represents the heat-sealableresin layer formed of random polypropylene.

DESCRIPTION OF REFERENCE SIGNS

-   -   1: Polyester Film    -   2: Adhesive agent layer    -   3: Barrier layer    -   4: Heat-sealable resin layer    -   5: Adhesive layer    -   6: Surface coating layer

1. A battery packaging material comprising a laminate that includes atleast a barrier layer, a heat-sealable resin layer situated on onesurface side of the barrier layer, and a polyester film situated on theother surface side of the barrier layer, the polyester film having aratio in a range of 1.4 or more and 2.7 or less between a maximum valueY_(max) and a minimum value Y_(min) (degree of surface orientation:Y_(max)/Y_(min)), with the maximum value Y_(max) and the minimum valueY_(min) respectively representing a maximum value and a minimum value ofa ratio between an absorption peak intensity Y₁₃₄₀ at 1340 cm⁻¹ and anabsorption peak intensity Y₁₄₁₀ at 1410 cm⁻¹ (Y₁₃₄₀/Y₁₄₁₀) in infraredabsorption spectra acquired for 18 directions at intervals of 10° from0° to 180° on a surface of the polyester film according to attenuatedtotal reflection of Fourier transform infrared spectroscopy.
 2. Thebattery packaging material according to claim 1, wherein a ratio ofthickness of the heat-sealable resin layer to thickness of the polyesterfilm is less than
 3. 3. The battery packaging material according toclaim 1, wherein the heat-sealable resin layer has a thickness of 100 μmor less.
 4. The battery packaging material according to claim 1, whereinthe polyester film has a birefringence index of 0.016 or more.
 5. Abattery comprising: a battery element that includes at least a positiveelectrode, a negative electrode, and an electrolyte; and packaging thatis formed of the battery packaging material according to claim 1 andstores the battery element therein.
 6. A method for producing a batterypackaging material, the method comprising: a step of obtaining alaminate by laminating at least a polyester film, a barrier layer, and aheat-sealable resin layer in this order, and using, as the polyesterfilm, a polyester film having a ratio in a range of 1.4 or more and 2.7or less between a maximum value Y_(max) and a minimum value Y_(min)(degree of surface orientation: Y_(max)/Y_(min)), with the maximum valueY_(max) and the minimum value Y_(min) respectively representing amaximum value and a minimum value of a ratio between an absorption peakintensity Y₁₃₄₀ at 1340 cm⁻¹ and an absorption peak intensity Y₁₄₁₀ at1410 cm⁻¹ (Y₁₃₄₀/Y₁₄₁₀) in infrared absorption spectra acquired for 18directions at intervals of 10° from 0° to 180° on a surface of thepolyester film according to attenuated total reflection of Fouriertransform infrared spectroscopy.
 7. A polyester film used in a batterypackaging material, the polyester film having a ratio in a range of 1.4or more and 2.7 or less between a maximum value Y_(max) and a minimumvalue Y_(min) (degree of surface orientation: Y_(max)/Y_(min)), with themaximum value Y_(max) and the minimum value Y_(min) respectivelyrepresenting a maximum value and a minimum value of a ratio between anabsorption peak intensity Y₁₃₄₀ at 1340 cm⁻¹ and an absorption peakintensity Y₁₄₁₀ at 1410 cm⁻¹ (Y₁₃₄₀/Y₁₄₁₀) in infrared absorptionspectra acquired for 18 directions at intervals of 10° from 0° to 180°on a surface of the polyester film according to attenuated totalreflection of Fourier transform infrared spectroscopy.
 8. A methodcomprising applying, according to attenuated total reflection of Fouriertransform infrared spectroscopy, a polyester film in a battery packagingmaterial, the polyester film having a ratio in a range of 1.4 or moreand 2.7 or less between a maximum value Y_(max) and a minimum valueY_(min) (degree of surface orientation: Y_(max)/Y_(min)), with themaximum value Y_(max) and the minimum value Y_(min) respectivelyrepresenting a maximum value and a minimum value of a ratio between anabsorption peak intensity Y₁₃₄₀ at 1340 cm⁻¹ and an absorption peakintensity Y₁₄₁₀ at 1410 cm⁻¹ (Y₁₃₄₀/Y₁₄₁₀) in infrared absorptionspectra acquired for 18 directions at intervals of 10° from 0° to 180°on a surface of the polyester film.
 9. The battery packaging materialaccording to claim 1, wherein the thickness of the polyester film is 12to 50 μm.
 10. The battery packaging material according to claim 1,wherein an adhesive layer is provided between the barrier layer and theheat-sealable resin layer, and the thickness of the adhesive layer is0.1 to 20 μm.
 11. The battery packaging material according to claim 1,wherein an adhesive layer is provided between the barrier layer and theheat-sealable resin layer, and the thickness of the adhesive layer is 10to 50 μm.
 12. The battery packaging material according to claim 1,wherein a base material of the laminate is a single layer of thepolyester film.